1. Field of the Invention
The present invention relates to Printed Circuit Board (PCB) technology, and in particular relates to a PCB and an electronic apparatus having two or more types of pad structures.
2. Description of the Related Art
As electronic equipment technology continues to develop, more and more integrated circuit (IC) packages with small space are needed for electronic equipment. A Fine-Pitch Ball Grid Array (FPGA) is one key of fine chip scale package technology.
Presently for FBGA technology, pins of ICs for Printed Circuit Boards (PCBs) typically fully employ Solder Mask Defined (SMD) pad structure or fully employ Non-Solder Mask Defined (NSMD) pad structure. The SMD structure utilizes solder mask to control dimensions of pads. Since the size of the opening of the solder mask is smaller than the dimensions of copper roofing, the solderable pad size is equal to the dimensions of the solder mask opening. As for the NSMD structure, the NSMD structure utilizes copper roofing to control the dimensions of the pads. Since the size of the opening of the solder mask is greater than the dimensions of the copper roofing, the solderable pad size is equal to the dimensions of the copper roofing opening.
Although PCBs which fully adopt the SMD structure for pads can provide better pad size control, the dimensions of the pads have to be increased due to all pads adopting the SMD structure. Thus, the outing line rate for IC layout is decreased, leading to an increase in the dimensions of the PCB and IC, which increases the fabrication costs for the PCBs. On the contrary, when PCBs fully adopt the NSMD structure for pads, the outing line rate for IC layout can be increased. However, IC layout difficulty increases along with design constraints. Further, for power/ground pin pads, routing wires are required to be thick and the number thereof is required to be a large number. In this case, pad size control is made more difficult. Accordingly, the sizes of PCB pads may be different, leading to a decrease in fabrication success rate when utilizing Surface Mounted Technology (referred to as SMT), and increasing solder bridge and short-circuit issues for ICs.
Accordingly, when PCBs fully adopt the SMD structure for pads, the pad out-of-line rate decreases and PCB costs increases. Whereas when PCBs fully adopt the NSMD structure for pads, difficulty in the control of the pad size increases, which leads to increased inconsistencies, leading to solder bridge and short-circuit issues for ICs.